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Help! Mini Mil Power Supply on Life Support.

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Captain Jerry:

The power supply on my HF Mini Mill is on it's last legs.  Some days it is ok but on other days, not so much.  My electronics expertise is just above zero so I need help.  There are two controls. One is a big red on/off switch.  When I turn it on, two pilot lights come on, an orange one above the on/of switch, and a green one above the speed control.  The fan in the power control box at the top rear of the column also comes on (slightly noisy). 


The other control is a rotary speed control. The spindle rotates and speed increases with nob position.  I generally stop the  rotation with the speed knob for minor repositioning.  I alway stop rotation and turn off the on/off switch for tool changes or workpiece changes.


Over the last few days, getting the spindle to rotate after the switch has been turned of and back on has become unreliable.  Some times it will turn and sometimes it won't. Some times a few on/off flicks encourage it to go.  Other times it will not re-start until it gets damn good and ready.  I have some words that I use with the dogs when they behave that way but so far I have not find the magic word for the mill.  In fact, yesterday I was trying all of my magic words loudly and repeatedly while flicking the switches like a madman and one of the dogs bumped the shop door open to see if she was in trouble.


So where do I start short of replacing the whole thing?

Don1966:
Captain Jerry you never said if the lamps are turning on or off when you operate the switch. From what your saying it seems to be the switch that is the problem. It is pretty rare for the electronics to operate like the problem your have, not to say that it can’t but unlikely. If you have a fuse in the circuit check to see if it is loose in its socket. I would try replacing the power switch. I woul also check the wire connections from your power cable and to power switch.


Regards Don

Captain Jerry:
Thanks for replying Don.  To clarify, both lights come on with the power switch and the fan in he power supply box comes on, but even with the lights on, the spindle speed control may or may not work, so I don't think it is the switch.  The switch is a double pole mechanism and all contacts are clearly visible if I open the cover,  They all look clean and bright.  There is a fuse in a cartridge holder and the first time I checked it, it looked good but the spindle ran when I replaced the cartridge holder.  I thought I had found where the problem was located but fiddling with the fuse holder has not worked since then.


I agree that electronic component failure is not usually intermittent unless related to heat.  This does not seem to be heat related. I may be able to work it for long periods without it failing.  It has never failed while in use.  It only fails to start from time to time.  To rule out a dead spot in the motor, I have rotated the spindle by hand when it is in a failed state with no response.


Getting into the power supply box is a bitch.  I have to unbolt the mill from bench and turn it around because is only inches away from the wall. Cables and plugs and outlets are all in good shape.

AOG:
One or more of the FETs in the power supply board are probably dead. It’s a fairly common problem with aging chinesum mini lathe/mill electronics. If you’re not good with electronics you can just replace the board. If I remember correctly LMS carries them. If it’s not too bad, there are a couple of things you can do to keep running in the short term. Try turning it on with the speed dial set about midway. If only one FET is down they will usually start that way. If that doesn’t work try manually start it with a flick on the chuck. It may stay running. In both cases that is a temporary fix. The lathe is down on power and if you push it to hard you will burn up the board the rest of the way.

Tony

Captain Jerry:
thanks, Tony. I'll give that a try/

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